TransCore MPRX Series - Chapter 4 Communications Protocols; Introduction

Chapter4 Communications Protocols
Introduction
The MPRX supports the following communications protocols:
• Basic
• Error correcting
• Data inquiry
The following protocol information provides reference information relevant to developing host software.
Communications are performed using the 7-bit ASCII code with optional parity, providing easy setup,
testing, and diagnostics with standard ASCII terminals and serial printers.
Each message is framed within the start-of-message <som> and end-of-message <eom> characters
so that the host device can detect the beginning and end of each message. This convention is most
important under marginal communications conditions during which the host may receive extraneous noise-
induced characters between reader transmissions. In such instances, the host is capable of ignoring any
messages that do not conform to the <som>...<eom> frame sequence.
Both data mode and command mode require a two-way message interchange when using error
correcting protocol (ECP). This interchange is completed by the message recipient returning a message
acknowledgment to the message sender.
With ECP, all transmissions require a message. If a message is not received, the sender will time out with
the same eect as if it had received a negative acknowledgment (from the host) or an #Error message
from the MPRX.
Software (XON/XOFF) flow control is optionally supported. Be careful in the use of XON/XOFF since noise-
induced characters may be interpreted by the MPRX as the XOFF character, which would suspend reader
output without information reaching the host device. For more information, refer to “Reader Transmissions”
on page 4–44.
Note: TransCore recommends that XON/XOFF flow control be disabled while using ECP.
MPRX User Guide
TransCore Proprietary
4–42